Polyamide fiber has become the most popular synthetic material for carpets because of its outstanding combination of wear resistance, bulk, recovery from compression and easy dyeability. Nevertheless polyester fiber has captured a portion of the carpet market because of its low cost and resistance to staining from accidental spills of foods or beverages containing natural or artificial acid dyes. However, polyester carpet fibers tend, by comparison to nylon fibers, to have a slow uptake of disperse dyes and this to a large extent prevents polyester carpets from being dyed on continuous dye ranges where the dyeing cycle is relatively short such as a few mintues. In addition, the polyester carpet fibers are regarded as having poorer recovery from compression than do nylon fibers. The use of carriers had been somewhat successful in increasing the dye rates of polyester fibers, but this has proved in many instances today to be no longer ecologically acceptable for carpet mills. When attempts have been made to increase the rate of dye uptake of a fiber by the inclusion of a comonomeric constituent, e.g. glutaric acid when producing a poly(alkylene terephthalate) such as poly(ethylene terephthalate) (abbreviation 2GT), the already unsatisfactory recovery from compression of the fiber has become still worse. Furthermore, the amount of such a comonomeric constituent needed to give adequate fiber range dyeability has tended to depress the melting point to such a large extent that the fiber becomes difficult or impossible to spin on spinning machines which are directly coupled to continuous polymerization lines. Finally, such an amount of comonomeric constituent has also been found to depress the glass transition temperature of the fiber to such an extent that permanent pile distortion may occur when rolls of carpets are shipped or stored in non air-conditioned vehicles or storage areas during summer months. A polyester fiber having a faster dye uptake and better recovery from compression would be greatly desired, especially if this could be accomplished without compromising other important fiber properties such as melting point.
Accordingly, it is an object of the invention to provide an improved polyester fiber which is suitable for use as a carpet fiber by virtue of enhanced dyeability on continuous dye ranges and which has improved recovery from compression.